Patent GB-1158589-A (GB)
Title: Crossed-Field Discharge Device and Arrangement Using Same
IPC: H01J23/05
Filed: 1966-08-04
Abstract: 1,158,589. Transit-time tubes. GENERAL ELECTRIC CO. 4 Aug., 1966 [30 Aug., 1965], No. 35033/66. Heading H1D. A crossed-field discharge device includes a cathode axially mounted within an anode formed by an annular member which has a plurality of axially extending recesses cut into its inner surface, and axially extending conductive rods mounted within the recesses and con - ductively connected to the annular member, whereby the anode constitutes an axially extending transmission line within which, by conductively enclosing each end of the anode or by coupling a coaxial line thereto, respectively, axially directed waves may be generated or amplified at a frequency for which the radial dimensions of the cathode-anode space precludes the maintenance of radially directed waves. In the device of Figs. 3 and 5, the cathode 140 is coaxially mounted within an anode structure formed by a copper cylinder 111 having its inner surface axially grooved to provide recesses 116 within each of which is mounted a corresponding conductive rod 130, the emissive surface of the cathode being correspondingly grooved to provide grooves of twice the number of the anode recesses, the cathode grooves being circumferentially displaced by a small angle from the symmetrical position with respect to the opposed anode recesses. The rods are supported at their ends by the polepieces 120, which are insulated from the cathode by ceramic insulators 145, and are sealed to the ends of the anode cylinder by members 125 of magnetic material, e.g. steel, the magnetic circuit for producing an axial unidirectional field being completed by magnetic yokes 132, 136, Fig. 2, flanges 133, 137, and outer casing 105, and energized by coils 131, 135. The cathode heater 151 is connected at end 152 to the cathode and at the other end to lead 62 of the A.C. heater supply. The device shown constitutes an oscillator, the structure defined by the anode block, the rods, and the end seals 125, forming a resonant cavity of shorted transmission line form, in which axial standing waves of wavelength substantially double the length of the cavity are maintained by interaction with the electrons spiralling out from the cathode under the influence of the magnetic field (Figs. 6 to 11, not shown). The cathode acts as an output probe, the outer and inner conductors 171, 181, Fig. 2, of the output coaxial line being capacitively coupled, respectively, to the tube 107 connected to the anode block, and the conductor 178 connected to the cathode. The cathode potential, and second lead of the A.C. heater supply, is connected to lead 61, and hence to conductor 178 via the rod 184 which is mounted within but is insulated from the inner conductor 186 of a second coaxial line, the outer conductor 174 of which is connected to the D.C. supply for the anode, to which it is connected by tube 107. The magnetizing current passes from lead 60, through coil 131, lead 134, coil 135, lead 138, and cooling fin 129 which is attached to the anode block. To isolate the microwave output from the D.C. supplies, conductors 184, 186 are designed as a # choke for the frequency of operation, and the separate conductors of each of the pairs 107, 171 and 178, 180 overlap one another by #. In a modified oscillator arrangement (Figs. 17 and 18, not shown) the output coaxial line is connected between the anode block and the rod assembly, the rods at their upper end supporting a plate (425) which is spaced from an opposed plate (445) supported by a conductor (444) extending through but insulated from the end of the envelope. When used as an amplifier (Fig. 15, not shown) the signal to be amplified is fed to one end of the device-which acts as an open-ended transmission line-via a coaxial line capacitively coupled to the cathode and the anode block; it is stated that satisfactory amplification may be achieved with an anode length only 1/10th the wavelength of the amplified signal. A modified form of cathode for the device is described (Fig. 16, not shown), of truncated conical rather than cylindrical form; it is stated that increased output or amplification, respectively, may be obtained by the use of this form of cathode, if the output is taken from that end of the device at which the base of the cathode cone is located. The excitation of radial modes of oscillation is prevented by arranging that the radial distance between the cathode surface and the outermost walls of the anode recesses is sufficiently small compared with the axial length of the device. Details of dimensions, modes of operation, and of operating characteristics, are given.